The objectives of the proposed research are three-fold: a. To develop electrode probes using insolubilized enzymes for the direct assay of substrates of biological importance directly in body fluids and tissues. Electrodes for urea, glucose, uric acid, 1-phenylalanine and others will be developed. b. To design electrodes that could be used for the assay of enzymes of clinical importance, such as cholinesterase, alkaline phosphatase, LDH and others. c. To develop an electrode for phosphate that could be used for the direct assay of phosphate in blood, and which could be used for the basic sensor in an electrode for alkaline phosphatase.